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estrus cycle

...receptivity is highest—this is the estrous period. Some animals (
e.g., dogs) are monestrous, having only one heat during a breeding season. Others (
e.g., ground squirrels) are
polyestrous: if not impregnated, they will come into heat repeatedly during the breeding season. Males can recognize a female in heat by smell; certain substances (pheromones) are secreted only at...

reproduction

...period (diestrus) and another preparatory proestrus phase. Mammals that breed only once a year are termed monestrous and exhibit a long anestrus; those that breed more than once a year are termed
polyestrous. In many
polyestrous species the estrous cycle ceases during gestation and lactation (milk production), but some rodents have a postpartum estrus and mate immediately after giving birth.